(1) Field of the Invention
The present invention relates to a transmission line interface circuit provided between a plurality of transmission lines and a piece of high bit rate data terminal equipment. Recently, a source of high bit rate data, such as an HDTV (high definition television) apparatus, has been developed, and such high bit rate data is expected to be transmitted through a plurality of transmission lines each having a transmission rate lower that the transmission rate of the source of high bit rate data. Typical applications of the transmission line interface circuit are a piece of terminal equipment and a switching unit in a multi-point television conference system.
(2) Description of the Related Art
Since the transmission lines and the source of high bit rate data respectively operate synchronized with different clock signals, the timing of each bit of synchronized data has to be changed when the data is transferred between a source of a high bit rate and a plurality of transmission lines. Namely, such a transmission line interface circuit receives data from a plurality of transmission lines synchronizing with clock signal in the respective transmission lines, transfers received data to the high bit rate data terminal equipment synchronized with a clock signal of the terminal equipment, receives data from the terminal equipment synchronized with the clock signal of the terminal equipment, and transmits received data through the plurality of transmission lines synchronized with the timing of the respective transmission lines.
In addition to the above, frame phases of transmission frames in the plurality of channels are required to be aligned in the transmission line interface circuit.
The size of construction for changing the timing of each bit of the data synchronized, is required to be small. However, conventionally, there is no compact construction for the transmission line interface circuit containing a plurality of channels of transmission lines, for changing the timing with which each bit of data is synchronized, and aligning frame phases in the plurality of channels.